The present invention relates to an objective lens drive unit for used in an optical disk apparatus or the like, an optical pickup apparatus having the objective lens drive unit built therein, an optical disk apparatus having the optical pickup apparatus built therein and a method of manufacture thereof, or more in particular to the same unit and the same apparatuses having an improved mass producibility and accuracy.
Also, the present invention relates to a tracking leaf spring array and a focusing leaf spring array for manufacturing a tracking leaf spring array and a focusing leaf spring array, respectively, built in the objective lens drive unit, and an injection molding die for manufacturing the objective lens drive unit.
An optical disk apparatus in which information is recorded or reproduced by radiating the laser beam on an optical disk mounts thereon an optical pickup apparatus for radiating the laser beam on the optical disk, receiving the laser beam reflected from the optical disk and converting it into an electrical signal. The optical pickup apparatus is composed of a light source, an objective lens drive unit and a photo detector. The focusing and tracking operation of the objective lens drive unit is controlled by the spring force and the electromagnetic force in such a manner as to correctly project the focal point of the objective lens on the optical disk.
The conventional objective lens drive unit described above has the following problems. Specifically, even in the case where the objective lens drive unit is mass produced, the requirement for as many insert molding steps as the intended products makes it impossible to improve the production efficiency. Also, the tracking leaf spring 24 (see FIG. 3) is so thin and small that it cannot be easily handled for insertion into a cavity, which is another factor of low productivity. Further, a spring made of resin easily develops a tilt or is easily affected by secular variations.
A method is known, in which a tracking leaf spring and a focusing leaf spring may be made of the same material and bent together, forming an integral unit. In the unit thus made, the tracking leaf spring has a strain and can hardly attain dynamic characteristic which is axisymmetric. This means that the tracking leaf spring cannot take a correct dynamic behavior in an optical pickup and can hardly process signals correctly in an optical disk apparatus.
The two focusing leaf springs 22 (see FIG. 3), on the other hand, are preferably completely parallel to each other or have the central portion thereof slightly expanded, in consideration of the operation thereof as a parallel link mechanism. In view of this, a small step is formed in the cavity to provide the pair of the focusing leaf springs 24 with an expanded central portion. Nevertheless, it is difficult to form a small step or a desired shape, with high precision.